As far as I know there are a whole lot of different ways to use reverse breathing. A lot of different Images, Intentions and aims. So it is also used for packing qi in the abdomen.
Another aspect of reverse breathing can be to concentrate the qi while breathing in into the dantian.
And to expand the qi while breathing out onto the surface of the body, i.e. the skin.
And if this works, to expand the qi further, like the bubbles sprinkling out from a soda.

To my experience the most difficult part of reverse breathing before it comes to images or intent is first to really manage the physical part of contracting and expanding the abdomen. (Not the chest.) Because as far as I understand it, this is about actively and correctly moving the diaphragm, the pelvic diaphragm and the inner mucles of front and the back. Which is not easy to do.